Structure-reactivity relationship for fluorescence quenching of trans-stilbene by tertiary amines

Abstract

The quenching of rans-stilbene fluorescence by ten amines of formula (CH 3) 2NCH 2R in n-hexane has been examined. There is an excellent linear free energy relationship between the Stern-Volmer quenching constants and the inductive substitutent constants σ 1, giving a slope ϱ of −1.24 and a correlation coefficient of −0.997 for amines with RH, CHCH 2, Ph, CCH, CCCH 3, CO 2Et or CN. The negative and small absolute value of ϱ is indicative of a mechanism involving exciplexes with a moderate degree of charge transfer character (contact ion pairs) with partial positive charge on the amines molecules.